Year

2014

Degree Name

BEnvi Sci Hons

ANZSRC / FoR Code

059999 Environmental Sciences not elsewhere classified

Department

School of Earth & Environmental Sciences

Advisor(s)

Dianne Jolley

Abstract

Although recognised as a nonessential metal, aluminium was long considered virtually innocuous to marine organisms, largely because of the very low concentrations of aluminium naturally occurring in the marine environment. It is now clear however, that human activities are contributing to elevated concentrations of aluminium in industrialized harbours and coastal waters of Australia, which have the potential for adverse impacts on marine organisms. Toxicity testing recently conducted on a suite of marine algae, invertebrates and fish to derive a new ANZECC water quality guideline trigger value for the protection of organisms from aluminium identified marine diatoms (Bacillariophyceae) were amongst the most sensitive species to aluminum.

The overall aim of this study was to relate aluminium sensitivity for three species of marine diatoms (Ceratoneis closterium, Minutocellus polymorphus, and Phaeodactylum tricornutum) to aluminium speciation and investigate the mechanisms of toxicity of aluminium to the diatoms. The three diatoms differed in physical characteristics to investigate whether differences in sensitivity were influenced by biotic factors, such as the ultrastructure of the cell wall, cell shape or cell size. In addition total and dissolved (0.45 µm and 0.025 µm filtered) aluminium in the bioassays were measured over time to determine the forms of aluminium associated with observed effects.

There was a varied response in growth rate sensitivity to aluminium between diatom species with the most sensitive species being C. closterium (72-h exposure inducing 10% inhibition of growth rate (72-h IC10) = 80 (55-100) µg Al/L (95% confidence limits)) followed by M. polymorphus (72-h IC10 = 540 (460-600) µg Al/L) and P. tricornutum (72-h IC10 = 2100 (2000-2200) µg Al/L) based on time averaged concentrations of measured total aluminium. Toxicity in the most sensitive diatom, C. closterium, was shown to be due to the dissolved aluminium forms of aluminate (Al(OH)4-) and aluminium hydroxide (Al(OH)30), while both dissolved and precipitated aluminium contributed to toxicity in M. polymorphus. In contrast, aluminium toxicity to P. tricornutum was due to precipitated aluminium. Interspecies differences in aluminium sensitivity were not related to cell size or cell shape. A relationship between the ultrastructure of cell walls and aluminium toxicity was observed, with the two diatoms with a siliceous cell wall being more sensitive than the diatom with the weakly siliceous cell wall. Sensitivity of C. closterium and M. polymorphus was influenced by initial cell density, with aluminium toxicity increasing with increasing initial cell density. No effects on plasma membrane permeability were observed for any of the species suggesting mechanisms of aluminium toxicity to diatoms do not involve compromising the plasma membrane.

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